The cleanup of acid gases, such as CO2, from natural gas has been an extensively practiced technology. The industrial removal of CO2 from natural gas dates back to the 1930's. While several technologies exist for the removal of acid gases, one of the most commonly employed practices is the use of aqueous amines. In this process the amine reacts with the CO2 to form a carbamate or bicarbonate salt along with a protonated amine to balance the overall charge. The liquid, CO2 rich amine from the bottom of the absorber, is then passed through a heat exchanger to improve efficiency before being heated to a higher temperature in a stripper. The stripper removes the CO2 as a gas from the amine solution to produce a lean, or CO2 deficient solution. The lean solution is returned to the absorber by way of the heat exchanger to repeat the process.
The application of CO2 capture and storage (CCS) to post-combustion flue gas separation has recently been an area of major interest. Due to the maturity of aqueous amine carbon capture systems, this technology will be the preferred method when new regulations require widespread full-scale deployment of post-combustion CCS for reducing emissions from fossil fuel combustion.
With continued societal and regulatory concern over the global climate change, the market has been driving the post-combustion capture technology development towards commercial scale. However, there is still a need for significant technological advancements and cost reduction strategies to make these systems cost-competitive. Full scale implementation of current carbon capture systems is estimated to increase the overall cost of electricity by 85% ($66/ton CO2 captured) over a twenty-year levelized cost, with the largest contributing factor being the capital cost to build the absorber tower. Absorber tower height is directly related to the CO2 absorption rate that is influenced by reaction kinetics, active gas-liquid contact surface, and CO2 driving force. There has been significant effort toward increasing the mass transfer (KG) of CO2 in the absorber by selecting fast kinetic solvent, intensifying gas/liquid mixing and modifying solvent properties to improve the effectiveness of gas-liquid contact surface.
This document relates to a new and improved method and apparatus for increasing mass transfer in gas separation processes that utilize aqueous solvents with a custom packing material that is designed to increase turbulent liquid flow then freshen the gas-liquid interface with unreacted bulk chemicals, which is known to increase overall KG. With an enhanced KG or absorption rate, the residence time to reach target capture efficiency will be decreased, requiring a shorter absorber tower and a lower capital cost. In addition, higher solvent loadings may be reached to reduce the requirement of CO2 stripping carry gas with increased mass transfer thereby lowering stripper energy requirements.
Advantageously the new and improved method and apparatus are applicable to any solvent based gas separation process, including post combustion CO2 capture, where mass transfer is limited by physical diffusion.